Multi-point shape optimization of airfoils at low Reynolds numbers

Abstract

A continuous adjoint method is formulated and implemented for the multi-point shape optimization of airfoils at low Re. The airfoil shape is parametrized with a non-uniform rational B-Spline (NURBS). Optimization studies are carried out for two different objective functions. The first involves an inverse function on the lift coefficient over a range of Re. The objective is to determine a shape that results in a lift coefficient of 0.4 at three values of Re: 10, 100 and 500. The second objective involves a direct function on the lift coefficient over a range of angles of attack,α . The lift coefficient is maximized simultaneously for α = 4° , 8° and 12° while the Re is held constant. The final shapes from both the cases are compared with those from the single-point optimization at each of the operating point. It is seen that the multi-point shapes are significantly different. They also have a better off-design performance than the geometries from single-point designs.